(1) Field of the Invention
The present technology relates to a fusing device and an image forming apparatus using this, in particular relating to a fusing device including a cleaning device of a web-cleaning type for cleaning the surface of a rotating roller member by pressing a web material against the outer peripheral surface of the roller member as well as to an image forming apparatus for performing printout of images by fixing toner images onto recording media using the above fusing device.
(2) Description of the Prior Art
Conventionally, in an image forming apparatus such as a facsimile machine, printer, etc., using electrophotography, image forming is performed by electrifying a rotationally driven photoreceptor drum with a charger, forming an electrostatic latent image on the photoreceptor drum by light irradiation of image information, forming a toner image by adhering toner to the electrostatic latent image and transferring the toner image onto a recording medium such as a sheet medium, paper or the like.
In this image forming apparatus, a fusing device for fusing and fixing unfixed toner onto the recording medium being conveyed is provided. Most of such fusing devices include a pair of roller elements, namely a heat roller and a pressing roller, disposed at the position where the unfixed toner is fused and fixed, or in essence, use a thermal fusing roller process, in which the toner on the recording medium is imparted with heat through the press-contact area (fusing nip portion) between these two rollers so as to fix the toner to the recording medium.
In the fusing device thus configured, the unfixed toner is fused and fixed through the fusing nip between the heat roller and pressing roller. However, all the toner cannot be fixed to the recording medium during this fusing process, hence part of the toner in its fused condition adheres to the heat roller surface and remains thereon, so that it will turn with the heat roller. If a next printing operation is performed under this condition, there occurs the problem that the paper is dirtied on the backside and/or on the printed side.
To deal with this, as a mechanism for reducing the toner that has adhered to and remains on the heat roller surface, a cleaning device of a so-called web-cleaning type that cleans the roller surface by applying a web material over the heat roller has been known.
For example, as a conventional technology there has been a cleaning device which, in order to perform stable cleaning, includes a crown-shaped or counter-crown-shaped heat roller and a pressure roller for applying the web material against the heat roller in the form of a counter-crown shape or crown shape corresponding to the aforementioned shape of the heat roller, to thereby prevent the web material from skewing (see patent document 1: Japanese Patent Application Laid-open Hei08 No. 87194).
However, the known cleaning device using the conventional web-cleaning technique is adapted to perform end detection of the web sheet by using metal conduction, and there has been the problem that this sensor for end detection exerts influence on the web sheet.
For example, as a conventional technology shown in FIGS. 1A, 1B and 1C, there is a known configuration in which when end detection of a web sheet 121 is carried out in a conventional cleaning device 120A, a web detecting terminal (end detecting terminal) 126 arranged adjacent to a metal guide roller 124 for guiding conveyance of web sheet 121 in a unit case 120a is used. A reference numeral 122 in the drawing designates a pressure roller, 127 a web sheet delivery roller for supplying web sheet 121, and 128 a winding roller for winding up web sheet 121. An arrow A in the drawing represents the direction in which web sheet 121 is conveyed.
In this configuration, strain arises in web sheet 121 (area E) on the downstream side, with respect to the web sheet's direction of conveyance, of pressure roller 122 as shown in FIG. 1B, on the side where web detecting terminal 126 is arranged while a slack arises in area F of web sheet 121 where no web detecting terminal 126 exists, as shown in FIG. 1C.
Because strain and slack occur at the same time across web sheet 121 due to influence of this web detecting terminal 126, there occurs the problem that rumples 121a and skewing arise in web sheet 121 as shown in FIG. 1A, giving rise to the cause of cleaning failure.